After replacing an alternator in a vehicle the alternator still isn’t functioning properly, what is the cause?
In a 1998 Dodge Durango 5.2L the car was experiencing dead battery problems, we performed the “Bad Alternator Test” where we pulled the negative off of the terminal and the vehicle stalled proving the alternator was bad. We then replaced the alternator and performed the test again and it failed again. What else could cause the problem?
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first thing first ! make sure there is power going to the alternator ! it could be a burnt fusible link or the plug-in is bad that connects to the alternator ! you need to test the wire going to the alternator to make sure there,s juice getting to the alternator ! if there,s no juice getting to the alternator then it can,t do its job ! just a reminder ! unhooking the battery when it,s running is a good way of messing up the computer ! you can,t do stuff to these new cars like you could on the old cars without a computer !
The other answers already said this and they are right, but I just have to add it again because it is so important.
NEVER remove a battery terminal from a running car.
What is supposed to happen when you do that is burn up the alternator because it will be trying to charge against something that isn't there. No battery is like one that is really, really dead, so needs the maximum charging.
The way you are supposed to check an alternator is to just put the leads of a voltmeter across the battery. Then it should read 12.5. After starting and reving slightly, it should go over 14 volts. If it does, it is fine. If it does not move at all, and stays 12.5, you could have lack of current to the field input of the alternator. For example, on Bosch systems the field current comes through the dash battery light. All alternators need current in before they can work because they have no permanent magnets like generators do. So a burned out dash battery light bulb can prevent the alternator from working.
If you really don't have a voltmeter and don't want to spend the $3 to get one at Harbor Freight, then an alternative is to watch the headlights brighten slightly when reved vs idle.
That is a very poor test for a bad alternator with an electronic fuel injection. Take the old alternator to a parts store and have them test it. I would guess that the alternator is not the problem. It could be the wiring for the alternator.
You did not perform squat! All you did was put the alternator into maximum output and probably fried it by taking the battery cable off! You always need to charge and test a battery before thinking you have a bad alternator. Keep "playing mechanic" and next you will find out pumping 16 volts or more through your cars electrical system with the battery out of the system also fries all your computers. You're well on your way to making thousands of dollars worth of damage because of foolish things you're doing!!
WHAT A MORON. THAT IS A BAD OWNER TEST NOT AN ALTERNATOR. THE CAR SHOULD FAIL WITH THE NEGATIVE REMOVED
What could be the problem.... ? ................... YOU
you should never un-hook the battery cable, on a running engine ,...to do a " test "...the battery acts as a buffer for voltage spikes,.................. even if its " dead "